In a conventional bicycle multi-gear rear cassette, a plurality of sprockets of variable diameter are axially distributed along and co-axially mounted to a freehub body. Each sprocket has a plurality of teeth about its perimeter for engaging a bicycle chain. For example, a mountain bicycle rear cassette with ten sprockets, S1-S10, could have sprockets with the following teeth (T) profiles: 11T, 13T, 15T, 17T, 19T, 21T, 24T, 28T, 32T, and 36T (i.e., 11T to 36T). When a shift control device is actuated by a bicyclist, a rear derailleur transfers the chain from the teeth of one sprocket to another.
To reduce the weight of the cassette, a sprocket carrier has been used to support a plurality of sprockets. A relatively low density metal such as aluminum is typically used for the carrier, while various types of steel materials provide the sprockets with adequate strength. The carrier comprises a plurality of radially extending mounting arms. Each mounting arm includes a sprocket mounting portion. Fasteners, such as bolts, mating threads, coupling projections, rivets, and the like, are used to fasten the sprockets to the sprocket mounting portion of the carrier. These mechanical connections not only require additional materials making the sprocket assembly heavier, but also weaken the mating parts and provide possible fatigue and fracture failure points on both the sprockets and carrier. Further, such mechanical connections introduce additional unwanted flexibility as they twist and deform under loading.
It may be desirable to increase the number of sprockets available in a bicycle multi-gear rear cassette to provide the bicyclist with a greater choice of gears. In relatively recent years, the number of sprockets in a typical mountain bicycle multi-gear rear cassette has increased from nine to ten sprockets. Even more recently, the number of sprockets has increased from ten to eleven. By increasing the number of sprockets, the bicyclist may be able to increase the range of the multi-gear rear cassette (i.e., the ratio derived from dividing the teeth profile of the sprocket having the largest diameter by the teeth profile of the sprocket having the smallest diameter) thereby providing the bicyclist with a greater range of gears to choose from. Thus, the range of a typical mountain bicycle multi-gear rear cassette having ten sprockets ranging from 11T to 36T has a range of 327%, which is greater than the range of a typical mountain bicycle multi-gear cassette having nine sprockets ranging from 11T to 34T (i.e., a 309% range). The range of a typical mountain bicycle multi-gear cassette having eleven sprockets ranging from 10T to 42T is greater still (i.e., 420%).
While a drivetrain having an eleven sprocket rear cassette is advantageous to bicyclists due to the enhanced range, an eleven sprocket rear cassette is incompatible with drivetrains designed for use with nine or ten sprocket rear cassettes. For a bicyclist to install an eleven sprocket rear cassette on a bicycle having a drivetrain using a nine or ten sprocket cassette, the bicyclist must purchase and install a new bicycle chain, rear derailleur, shift control device, and/or front chain rings. This can be prohibitively expensive.
There is a general desire to increase the range of gears available to a bicyclist without the bicyclist having to make substantial changes to the drivetrain and/or considerably increasing the weight of the bicycle.
The foregoing examples of the related art and limitations related thereto are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.